The invention relates to a double-stranded ribonucleic acid (dsRNA) forinhibiting the expressionof a Hepatitis B Virus gene. The invention also relates to a pharmaceuticalcompositioncomprising the dsRNA or nucleic acid molecules or vectors encoding the sametogether with apharmaceutically acceptable carrier; methods for treating diseases caused byHepatitis B Virusinfection using said pharmaceutical composition: and methods for inhibitingthe expression of aHepatitis B Virus gene in a cell.